Merchant marine officers work shifted hours with a sometimes very tiring work/rest rhythm that can lead to sleep restrictions and increased sleepiness during navigation. The aim of this study is to assess the risk of sleep deprivation-related sleepiness during navigation and the factors contributing to this risk. A second objective is to evaluate the use and effectiveness of sleepiness countermeasures. An online quantitative survey of 43 questions was conducted on 183 French maritime officers. A total of 39.9% of the participants experienced at least occasionally severe sleepiness and 29% had fallen asleep during navigation. A total of 42.6% reported not being able to experience enough sleep on board. Sleep requirements were affected by time spent on board, area of activity, and watch system. Sleepiness was more common during monotonous than demanding sailing. Officers frequently use caffeine, as well as vigilance-enhancing activities that they consider effective, which are not yet validated, (i.e., social interactions). However, they are not inclined to seek replacements in case of severe sleepiness. Sleep deprivation is common among maritime officers and leads to the risk of severe sleepiness while operating the vessel, with few effective countermeasures available. Strategies used for sleep management and sleepiness prevention should focus more on sleep duration, safety culture, and improving countermeasures to sleepiness.